Ankle-Brachial Index Calculator

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Walk-through

How to Use This Calculator

4 steps

1

Measure systolic blood pressure at both ankles and both arms

Using a blood pressure cuff and a handheld Doppler (or an automated ABI device), measure systolic blood pressure (SBP) at the left ankle (posterior tibial or dorsalis pedis artery, use the higher of the two), the right ankle, and both arms (brachial artery).

2

Enter the four pressures

Enter left ankle SBP, right ankle SBP, left brachial SBP, and right brachial SBP into the calculator. The ABI tab updates instantly as you type.

3

Read the ABI and severity tier

The ABI tab shows both legs' ABI side by side. Each ankle pressure is divided by the higher of the two brachial readings, per AHA/ACC methodology. Open the Severity Tier tab to see the reference table with the matching row highlighted for whichever leg you select.

4

Check the Both Legs tab for inter-limb comparison

The Both Legs tab shows a side-by-side summary and flags whether the difference between legs is itself clinically meaningful (a gap greater than 0.15 between left and right ABI). Use Share or Copy to save a reading; your numbers are encoded in the URL.

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Reference

Formula & Methodology

1 formula

Ankle-brachial index (per leg)

ABI (leg) = ankle SBP (that leg) ÷ higher of (left brachial SBP, right brachial SBP)

The ankle-brachial index compares blood pressure at the ankle to blood pressure at the arm. Each leg's ABI uses that leg's own ankle systolic pressure as the numerator, but both legs share the same denominator: the higher of the two brachial (arm) systolic readings. Using the higher-of-both-arms reading avoids under-estimating ABI when one arm has its own subclavian or axillary artery narrowing, which would otherwise make that arm's pressure read artificially low.

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YMYL

Trust, Methodology & Sources

Reviewed by Calculover Editorial Review · Updated 2026-07-22 · 2 sources

Editorial accountability

Author: Calculover Editorial Team - Editor

Owner: Calculover Editorial Team - Editorial owner

Reviewer: Calculover Editorial Review - Medical-source review

Last reviewed: 2026-07-22

Last verified: 2026-07-22

Data effective: 2026-07-22

Methodology

The Ankle-Brachial Index Calculator applies the standard AHA/ACC formula per leg: ABI = ankle systolic blood pressure (that leg) ÷ the higher of the two brachial (arm) systolic blood pressure readings, which is used as a shared denominator for both legs to avoid under-estimating ABI when one arm's own reading is reduced by unrelated arterial disease. Severity tiers (severe PAD ≤0.40, mild-to-moderate PAD 0.41–0.90, borderline 0.91–0.99, normal 1.00–1.40, noncompressible >1.40) follow the 2016 AHA/ACC Lower Extremity Peripheral Artery Disease guideline.

Assumption: Ankle and brachial systolic pressures are entered for the same patient, measured at rest, at approximately the same point in time.

Assumption: Each ankle pressure represents the higher of the posterior tibial and dorsalis pedis readings at that ankle, and each brachial pressure is a standard arm cuff systolic reading.

Assumption: The user wants a screening estimate and severity classification, not a diagnosis, treatment plan, or a substitute for a vascular lab study.

Limitations & guidance

This tool performs the ABI arithmetic and classification only — it cannot verify that the underlying pressure measurements were taken correctly and does not replace a vascular lab study or imaging.

A resting ABI can be falsely normal in patients whose disease only becomes limiting during exertion; exercise ABI testing may be needed to unmask milder disease.

An ABI above 1.40 indicates noncompressible, calcified vessels rather than reliable results — common in diabetes and end-stage renal disease — and requires confirmation with a toe-brachial index or another modality.

This is a screening aid, not a diagnostic result. It does not diagnose, monitor, or guide treatment of any condition — always confirm findings with a qualified vascular clinician.

Professional guidance: The Ankle-Brachial Index Calculator is for health education and clinical decision support only. It provides an estimate based on user-entered values, not medical advice, diagnosis, or treatment, and is not a substitute for vascular lab confirmation or care from a licensed healthcare professional. Always rely on a qualified clinician for medical decisions.

Primary sources

Gerhard-Herman MD, Gornik HL, et al. 2016 AHA/ACC Guideline on the Management of Patients With Lower Extremity Peripheral Artery Disease. - Circulation

Aboyans V, Ricco JB, et al. 2017 ESC Guidelines on the Diagnosis and Treatment of Peripheral Arterial Diseases. - European Heart Journal

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Glossary

Key Terms Explained

7 terms

Ankle-brachial index (ABI) The ratio of systolic blood pressure at the ankle to systolic blood pressure at the arm, used to screen for peripheral artery disease. A value of 1.00–1.40 is considered normal.

Peripheral artery disease (PAD) Narrowing of the arteries that supply blood to the limbs, usually from atherosclerosis, which reduces blood flow to the legs and feet and can cause claudication, non-healing wounds, or limb-threatening ischemia in severe cases.

Brachial SBP Systolic blood pressure measured at the brachial artery in the upper arm — the standard arm blood-pressure reading. ABI uses the higher of the left and right brachial readings as the shared denominator for both legs.

Ankle SBP Systolic blood pressure measured at the ankle, using a Doppler probe over the posterior tibial or dorsalis pedis artery — whichever gives the higher reading at that ankle.

Noncompressible vessels Arteries so stiffened by calcification that a blood pressure cuff cannot fully compress them, producing a falsely elevated ABI (typically > 1.40). Common in diabetes and end-stage renal disease; requires a toe-brachial index or another modality to properly assess.

Vascular screening Non-invasive testing (such as ABI) used to detect arterial disease before it becomes symptomatic or to evaluate the cause of leg symptoms, without requiring imaging or invasive procedures.

Claudication Pain, cramping, or fatigue in the calf, thigh, or buttock brought on by walking and relieved by rest — the classic symptom of peripheral artery disease, caused by inadequate blood flow to exercising muscle.

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Scenarios

Real-World Examples

3 worked examples

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Healthy adult — routine screening

Ankle 130/128 mmHg, brachial 120/122 mmHg

Left ankle SBP 130 mmHg Right ankle SBP 128 mmHg Left brachial SBP 120 mmHg Right brachial SBP 122 mmHg ABI (left) 1.07 ABI (right) 1.05

Higher brachial SBP is 122 mmHg. Left ABI = 130 ÷ 122 = 1.07; right ABI = 128 ÷ 122 = 1.05. Both fall in the normal 1.00–1.40 range — no evidence of PAD from this reading.

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Claudication symptoms — one affected leg

Ankle 78/130 mmHg, brachial 130/128 mmHg

Left ankle SBP 78 mmHg Right ankle SBP 130 mmHg Left brachial SBP 130 mmHg Right brachial SBP 128 mmHg ABI (left) 0.60 ABI (right) 1.00

Higher brachial SBP is 130 mmHg. Left ABI = 78 ÷ 130 = 0.60, in the mild-to-moderate PAD range — consistent with the patient's claudication in that leg. Right ABI = 130 ÷ 130 = 1.00, at the low end of normal. The 0.40 gap between legs is itself a notable finding pointing to unilateral disease.

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Diabetic patient — noncompressible vessels

Ankle 190/185 mmHg, brachial 128/130 mmHg

Left ankle SBP 190 mmHg Right ankle SBP 185 mmHg Left brachial SBP 128 mmHg Right brachial SBP 130 mmHg ABI (left) 1.46 ABI (right) 1.42

Higher brachial SBP is 130 mmHg. Left ABI = 190 ÷ 130 = 1.46 and right ABI = 185 ÷ 130 = 1.42 — both above 1.40, flagged as noncompressible. This pattern is common in diabetes or end-stage renal disease, where arterial calcification stiffens vessel walls so the cuff can't fully compress them, producing a falsely high reading rather than true evidence of good blood flow. A toe-brachial index or another modality is needed to properly assess these patients.

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Deep Dive

Understanding the Ankle-Brachial Index

3 chapters · 5 min read

The ankle-brachial index is a simple, non-invasive ratio that compares blood pressure at the ankle to blood pressure at the arm — and it's one of the most widely used screening tools for peripheral artery disease. This guide explains how the ratio is calculated, why the higher-of-both-arms rule matters, what each severity tier means, and where the test's assumptions break down.

Why compare ankle pressure to arm pressure

In a healthy circulatory system, systolic blood pressure at the ankle is roughly equal to — or slightly higher than — systolic blood pressure at the arm, because pressure doesn't meaningfully drop as blood travels down an unobstructed artery. When the arteries supplying the leg are narrowed by atherosclerosis, ankle pressure falls relative to arm pressure, and the ratio between the two (the ABI) drops below 1.0. The further below 1.0, the more severe the arterial narrowing is likely to be.

Each leg is scored independently using its own ankle pressure, but both legs share the same denominator: the higher of the two brachial (arm) readings. This is deliberate — if one arm's own pressure reading is reduced by unrelated subclavian or axillary artery disease, using the lower arm reading as a leg's denominator would inflate that leg's ABI and mask real disease in the leg. Cardiac output and hemodynamic status can also influence absolute pressure readings, which is one reason ABI is interpreted as a ratio rather than relying on either pressure alone.

Reading the severity tiers

An ABI of 1.00–1.40 is considered normal. Values from 0.91–0.99 are borderline and may warrant a repeat measurement or exercise testing. An ABI of 0.90 or below is diagnostic of peripheral artery disease, and the guideline further subdivides that range: 0.41–0.90 is mild-to-moderate disease, often associated with claudication symptoms, while 0.40 or below indicates severe disease with a meaningfully higher risk of critical limb ischemia and warrants urgent vascular evaluation.

An ABI above 1.40 doesn't mean unusually good circulation — it flags noncompressible vessels, most often from arterial calcification in diabetes or chronic kidney disease. In these patients, the blood pressure cuff can't fully compress the stiffened artery, so the reading is unreliable and a toe-brachial index (which uses smaller, more compressible digital arteries) or another imaging modality is needed instead.

Limitations of a single ABI reading

ABI is a screening tool, not a diagnosis. A resting ABI can be falsely normal in patients with mild disease whose arteries only become limiting during exertion — exercise ABI testing (measuring before and after treadmill walking) can unmask disease that resting ABI misses. Calcified, noncompressible vessels — common in long-standing diabetes and end-stage renal disease — produce falsely elevated readings rather than falsely reassuring ones, which is why this calculator explicitly flags any value above 1.40. And because both legs share one brachial denominator, an unrecognized error in either arm reading affects both legs' scores. This calculator performs the ABI arithmetic and classification only; it does not replace a vascular lab study, imaging, or the judgment of a qualified clinician, especially for patients with symptoms, risk factors, or a borderline or abnormal result.

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Questions

Frequently Asked Questions

6 questions

What is a normal ABI range?+

An ankle-brachial index between 1.00 and 1.40 is considered normal. Values from 0.91–0.99 are borderline. An ABI of 0.90 or below indicates peripheral artery disease, and an ABI above 1.40 suggests noncompressible vessels rather than good circulation.

What ABI value indicates peripheral artery disease (PAD)?+

An ABI of 0.90 or below is diagnostic of PAD. Within that range, 0.41–0.90 is classified as mild-to-moderate disease (often with claudication symptoms), and 0.40 or below is severe disease associated with a substantially higher risk of critical limb ischemia and usually warrants urgent vascular evaluation.

What does a noncompressible ABI reading mean?+

An ABI above 1.40 means the ankle artery is too stiffened by calcification for the blood pressure cuff to fully compress it, producing a falsely high reading rather than evidence of healthy blood flow. This is common in diabetes and end-stage renal disease. A toe-brachial index or another vascular imaging modality is needed to properly assess these patients.

Which brachial (arm) reading does the calculator use?+

The calculator uses the higher of the left and right brachial systolic readings as the denominator for both legs' ABI, per AHA/ACC methodology. This avoids under-estimating a leg's ABI when one arm has its own reduced pressure from unrelated subclavian or axillary artery disease.

Why is diabetes mentioned as a caveat for this calculator?+

Diabetes (and chronic kidney disease) commonly causes medial arterial calcification, which stiffens the ankle arteries so a blood pressure cuff can't fully compress them. This produces a falsely elevated, noncompressible ABI reading that can mask real underlying PAD rather than ruling it out — so an ABI above 1.40 in a diabetic patient should prompt further testing, not reassurance.

Is ABI used only for diagnosis, or also for screening?+

Both. ABI is commonly used as a screening tool in patients with risk factors (age, diabetes, smoking, hypertension) or leg symptoms, and it's also used diagnostically to confirm and grade the severity of suspected peripheral artery disease. A single resting ABI can miss milder disease that only becomes apparent on exertion, which is why exercise ABI testing exists as a follow-up option.

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Ankle & Brachial Pressures